where \(x_p\)  is the value of the data or model at a given pixel, \(G_{data}\)  is the observed spectrum, \(\Delta G_{data}\)  are the observed uncertainties, and \(G_{model}\)  is the model presented in eq. REF . The most commonly used method for the minimisation of eq. REF  is Least Squares, as there are plenty of computer implementations [1]}, [2]}, [3]} to perform the fits very efficiently.
